With more than 30 million HIV-infected individuals, there can be few other more pressing biomedical priorities than to produce an effective vaccine for HIV. Given the important role that cytotoxic T lymphocytes (CTLs) and helper T lymphocytes (HTLs) play in controlling viral replication, it is critical that this vaccine stimulates these cellular responses. Current methods of detecting vaccine-induced immune responses include Intracellular Cytokine Staining (ICS), Enzyme-Linked Spot Forming Assays (ELISPOT), and tetramer-staining. ICS and ELISPOT can be carried out using peptides of 9-15 amino acids in length. However, depending on where the true epitope lies in the synthetic peptide, these peptide sets may not accurately the magnitude of the immune responses. Furthermore, the synthesis of tetramers is absolutely dependent on knowledge of the minimal optimal epitope. We therefore, propose to continue our definition of minimal optimal epitopes for common Indian rhesus macaque class I and II molecules. In Specific Aim I: We will identify peptides that bind to seven new MHC class I molecules that restrict SIV-specific epitopes. The highest frequency alleles which have not been characterized yet include Mamu-A *0402,-A *08, -A *1304, -A *1403, -B 812, -B *3003, and -B *5702. In Specific Aim II: We will identify peptides that bind to seven new MHC class II molecules that restrict SIV-specific epitopes. The highest frequency alleles which have not been characterized yet include Mamu-DPB1 *06, -DPB1 &10, -DQB1 *1801, -DRB1 *0306, -DRB1 *0309. -DRB1 *1003. and -DRB1 *1002. These minimal optimal epitopes will allow us to accurately measure immune responses in vaccinated and infected macaques using ICS and ELISPOT. Furthermore, we will make tetramers important for monitoring immune responses, sorting T cell populations, and detecting antigen-specific T cell in situ. We will also establish MHC peptide prediction tools, which will be made available to the entire scientific community. These types of reagents have been and will be critical to our understanding of AIDS pathogenesis and AIDS vaccine development. The specific tetramer reagents, the binding assays and the MHC prediction tools will greatly expand our capacity to study immune responses.